The invention is directed to encrypting and decrypting blocks of digital data, and more specifically, to a cipher method and device for the block-by-block conversion of a first digital block into a second digital block using at least one freely selectable control block, using an improved block cipher with double the key length and significantly increased cryptographic strength while still providing a mode for inter-operability with prior art systems.
The rapidly growing use of digital communication systems in commerce has spurred the need for cryptographic systems which are secure against popular “cryptoanalysis” or cracking techniques at least for a sufficient length of time. Prior art systems such as Massey, et al. U.S. Pat. No. 5,214,703 use a block cipher device which is suitable both for the encryption of plain text blocks and for the decryption of ciphertext blocks.
The prior art system of Kurdziel, et al. U.S. Pat. No. 6,108,421, which is commonly owned and has inventors in common with the present application, is directed to a scaleable block cipher device which is customizable and not vulnerable to standard cryptoanalysis techniques.
It is known to use multiple encryption to provide robust and enhanced security of the encrypted data. However, such multiple encryption schemes have disadvantages. Multiple encryption schemes require multiple iterations through a cryptographic system. In the case of duplicate hardware blocks, this doubles or triples the gate count and power consumption in hardware renderings. In cases where execution of a single block is repeated, the maximum speed that the cryptographic system can operate at will be reduced to one-half or one-third depending on the number of iterations required.
Additionally, multiple encryption schemes require that a cipher method not be a mathematical function known as a “group”. If a cipher method is a group, no security enhancement is obtained by using it in a multiple encryption scheme. The significance of this is that it is often impossible to conclusively prove a cryptographic system is not a group. Indeed, a cryptographic system that approximates the behavior of a group, to even a slight degree will suffer security vulnerabilities when used in a multiple encryption scheme.
Thus, there is a need for block cipher device which is scaleable and customizable and providing the all the enhanced cryptographic strengths of a multiple encryption scheme, but without the severe disadvantages associated with multiple encryption.
Accordingly, it is an object of the present invention to provide a novel scaleable block cipher device that is secure against available cryptanalysis or cracking techniques.
It is another object of the present invention to provide a novel block cipher device which provides enhanced security while maintaining compatibility with the prior art cipher devices.
It is still another object of the present invention to provide a novel block cipher device having double the cryptographic strength without a proportional increase in gate count of hardware renderings.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.